1. Field of the Invention
The present invention relates to a hydraulic, adjustable vibration damper, such as for motor vehicles, with a damping piston fastened to a piston rod, which damping piston divides the work cylinder into two chamber halves filled with damping fluid, whereby there is at least one pressure controlled valve located in a bypass which runs parallel to the valves of the damping piston, and an adjustment apparatus pressurizes a control body to control the bypass.
2. Background Information
Federal Republic of Germany Laid Open Patent Application No. 33 03 293 describes damping force regulation devices for telescoping shock absorbers on which there is an additional double-acting damping valve, which is incorporated into the damping piston itself. These damping valves are connected in series and can be separated from one another by means of a rotary disc valve. In a first valve position, only the valve of the damping piston is carrying a flow, so that a hard damping action can be achieved. In a second valve position, the valve in the damping piston and the additional valve both carry flows, so that a correspondingly mild damping characteristic can be achieved.
A disadvantage with such an embodiment is that the rotary disk valve must be pressurized by appropriate adjustment forces which are applied by an electrically operated positioning motor.
The prior art also includes adjustable vibration dampers, for example, German Patent No. 35 18 327, in which there is a coil in the upper portion of the piston rod. An armature can be moved axially in the coil, and a defined bypass opening can be formed between the upper and lower work chamber as a function of the current applied to the coil. However, vibration dampers with a magnetic coil are expensive to manufacture.